Most portable electronic devices such as laptop and notebook computers, mobile phones, and game devices have flat viewing screens unlike the cathode-ray-tube (CRT) monitors of conventional desktop computers. Nevertheless, users still generally expect the flat viewing screens to provide performance equal to that of CRT monitors. To meet this demand, computer manufacturers have sought to build flat panel displays (FPDs) offering superior resolution, color, and contrast, while at the same time requiring minimal power consumption. Liquid crystal displays (LCDs) are one type of FPD that satisfy these expectations. However, the liquid crystals of an LCD are not self-luminescent. Rather, the LCD generally needs a surface emitting device such as a backlight module which offers sufficient luminance (brightness) in a wide variety of ambient light environments.
Referring to FIG. 7, this is a side view of a conventional backlight module. The backlight module 10 includes a light source 11, a light guide plate 12, a diffuser 13, a prism film 14, and a reflector 16. The light guide plate 12 includes a light output surface 122, a bottom surface 123 opposite to the light output surface 122, and a light incident surface 121 and side surfaces (not shown) interconnecting the light output surface 122 and the bottom surface 123. The reflector 16 is disposed adjacent to the bottom surface 123. The diffuser 13 and the prism film 14 are stacked in that order on the light output surface 122. The light source 11 is disposed adjacent to the light incident surface 121, for facilitating efficient transmission of light beams emitted by the light source 11 to the light guide plate 12. A plurality of dots 124 is formed at the bottom surface 123, in order to reduce internal reflection of light beams and provide more uniform brightness.
In operation, light beams emitted from the light source 11 enter the light guide plate 12. Some of the light beams strike the bottom surface 123, are scattered by the dots 124 and/or reflected by the reflector 16, and then exit through the output surface 122. Other light beams directly exit through the output surface 122. The light beams that exit through the output surface 122 then transmit through the diffuser 13 and the prism film 14, and finally illuminate a liquid crystal panel (not shown).
However, some of light beams propagating within the light guide plate 12 strike the side surfaces, and a portion of the light beams scattered by the dots 124 and/or reflected by the reflector 16 also strike the side surfaces. Light beams striking the side surfaces are liable to leak out from the side surfaces and be lost. Thereby, the backlight module 10 may have low efficiency in the utilization of light beams.
What is needed, therefore, is a backlight module which can provide highly efficient utilization of light beams.